Feature: Add support for multiple env

[dearchap]

What type of PR is this?

(REQUIRED)

• feature

What this PR does / why we need it:

(REQUIRED)

Which issue(s) this PR fixes:

(REQUIRED)

Fixes #39

Special notes for your reviewer:

(fill-in or delete this section)

Testing

Updated existing tests

(fill-in or delete this section)

Release Notes

(REQUIRED)

Multiple env variables are supposed in tag definitions. As of now only urfave/cli supports flags with multiple envs

[abitrolly]

~nn_8 ?

[abitrolly]

This breaks API and I don't see how this feature is going to be used. Docs and example is needed, because it becomes not intuitive anymore. Maybe it is possible to have separate extensions for such things? To keep binary sizes and feature creep minimal?

Also, what happens for programs that use old non-array way of env specifiers.

I don't see what happens in this PR because there are no examples and docs.

[dearchap]

This breaks API and I don't see how this feature is going to be used. Docs and example is needed, because it becomes not intuitive anymore. Maybe it is possible to have separate extensions for such things? To keep binary sizes and feature creep minimal?

Also, what happens for programs that use old non-array way of env specifiers.

I don't see what happens in this PR because there are no examples and docs.

Yes it breaks API but most people I am assuming use the gen cmds to translate this to a particular cli libary so they wont be affected by this. This is not a new feature I am adding. Using ~ before a name caused the parser to ignore prefix and divider options for env vars. The only thing I am doing is extending this to be a string slice instead of a string.